Gas chromatography (GC) entails the analytical separation of a vaporized or gas-phase sample that is injected into a chromatographic column. The column is typically a metal, glass, or quartz tube containing a stationary phase (a coating or packing) formulated for chromatographic activity. The column is typically housed in a thermally controlled oven or may be heated directly by a heating element such as a resistive wire. A chemically inert carrier gas, such as helium, nitrogen, argon, or hydrogen, is utilized as the mobile phase for elution of the analyte sample in the column. Typically, the sample and carrier gas are separately introduced into a GC inlet coupled to the column head. In the GC inlet, the sample is injected into the carrier gas stream and the resulting sample-carrier gas mixture flows through the column. The typical GC inlet is configured for vaporizing an initially liquid-phase sample, and may provide a liner configured for performing pre-column separation as well. During column flow the sample encounters the stationary phase in the column, which causes different components of the sample to separate according to different affinities with the stationary phase. The separated components elute from the column exit and are measured by a detector, producing data from which a chromatogram or spectrum identifying the components may be constructed.
A single GC column may be inadequate for separating a target compound from a sample. In this case, a multidimensional (MDGC) GC system including two or more GC columns and respective downstream detectors may be utilized, such as a comprehensive two-dimensional (GC×GC) system. The different GC columns may have different characteristics such as length, inside diameter, and/or type of stationary phase material. For example, in a GC×GC system one column may include a polar stationary phase while the other column includes a nonpolar stationary phase. During an appropriate interval of time, a portion of the effluent from the first column containing a target compound may be diverted into the second column and ultimately to the corresponding second detector by implementing a heart-cutting technique as appreciated by persons skilled in the art.
Multidimensional GC systems may utilize fluidic switches for implementing heart-cutting, as well as for other operational modes such as flow spitting, backflushing, etc. Fluidic switches may operate in conjunction with, or may be integrated with, microfluidic devices designed to conduct sample and/or carrier gas flows to and from GC columns, detectors, and other components of a multidimensional GC system. Multidimensional GC systems may also utilize flow control devices, often electronic pneumatic controllers (EPCs), to regulate mass flow rates, forward pressures, and back pressures in relation to the columns and other fluidic devices.
It is generally difficult for users of GC systems to correctly configure a multi-column system involving the use of microfluidic devices and flow control devices such as EPCs. It is also difficult for users to apply microfluidics to compact or even oven-less GCs, as all current microfluidic devices must rely on a relatively large, forced convection GC oven (air bath) to facilitate column coupling and to prevent microfluidic devices from becoming cold spots in the sample path. Moreover, current GC instruments lack a fundamentally scalable design that would be useful for supporting the growing sophistication of analytical tasks enabled by microfluidics, such as multidimensional GC and multiple independent column heating zones.
In view of the foregoing, there is a need for GC components and methods that enable or facilitate the design and building of GC devices and systems that provide various functionalities to meet current and future requirements.